Release of galactosyltransferase from human platelets and a subset of
monocytes in culture
KE Hopper, AD Semler, GV Chapman and RA Davey
We show that human monocytes and platelets release considerable amounts of
galactosyltransferase (GT) in serum-free culture as measured by the amount
of incorporation of 3H-galactose into ovalbumin. Enzyme production was the
greatest among medium-sized mononuclear cells separated by counter-current
elutriation. The cells were adherent and positive for the monocyte-specific
monoclonal antibody FMC-32. The activity in the monocyte fractions was not
due to platelet contamination as shown from experiments in which platelets
or platelet antigens were eliminated. Cell viability decreased by less than
3% during the overnight culture, and results from cell disruption
experiments showed that the enzyme was not released from dead or dying
cells. Cycloheximide inhibited release during 20 hours culture.
Approximately 50% of the enzyme in the cell culture supernatant was
pelletable at 105,000 g. Platelets released the enzyme more rapidly than
did monocytes and were readily stimulated by thrombin to release more GT.
Thrombin also increased monocyte GT activity after overnight incubation,
but other stimulants, zymosan and lipopolysaccharide (LPS), decreased
release. We conclude that GT is released into culture supernatants by
platelets and by a subset of peripheral blood monocytes. These sources may
account for a significant proportion of the serum enzyme and may be
important in modification of extracellular carbohydrates during
inflammation and coagulation.
Volume 68,
Issue 1,
pp. 167-172,
07/01/1986
Copyright © 1986 by The American Society of Hematology
